Just recently set this up, in case anyone runs into this issue before the next release, without flipping to dev branch you just need to edit /lib/ubuntu/config.sh and add an entry for 11) since it stops at 10) ( as Sebastian mentions, this OS is newer than the release )
11)
php_ver="7.4"
x="*php5* *php7.0*"
;;
I also removed the reference to the package php-gettext as I read it was no longer required with PHP7.